Add public scoreboard slug & URL

test/models/contest_test.rb

@@ -5,6 +5,7 @@
 #  id                 :integer          not null, primary key
 #  allow_registration :boolean          default(FALSE)
 #  name               :string
+#  slug               :string
 #  team               :boolean          default(FALSE)
 #  created_at         :datetime         not null
 #  updated_at         :datetime         not null